Dosimeter using a fluorescent glass element

ABSTRACT

This dosimeter comprises a vessel having an inlet slit and outlet slit for ultraviolet rays and a slit for releasing fluorescent light beams which is opened in a direction almost perpendicularly intersecting the direction in which the ultraviolet rays are introduced. In said vessel is housed a trapezoidal fluorescent glass element whose operating plane is exposed to radiation in advance and so positioned as to face the ultraviolet-ray inlet slit and fluorescent light beam release slit and also to be inclined at an angle allowing for the total reflection of ultraviolet rays with respect to the direction in which they are brought in.

llnited States tent Yolrota et 31L [54] DOSIMETER USING A FLUORESCENTGLASS ELEMENT [72] Inventors: Ryosuke Yokota; Yuhei Muto, both ofYokohama-shi, Japan [73] Assignee: Tokyo Shibaura Electric Co., Ltd.,

Kawasaki-shi, Japan [22] Filed: June 16, 1969 [21] Appl. No.: 833,621

[30] Foreign Application Priority Data June 20, 1968 Japan ..43/42381[52] US. Cl. ..250/71.5 R, 250/83 CD 51 rm. Cl ..G0lt 1/06 [58] Field ofSearch ..250/71, 71.5, 83 CD [56] References Cited UNITED STATES PATENTS3,020,238 2/1962 Munakata ..250/83 X Primary Examiner-James W. LawrenceAssistant Examiner-Davis L. Willis Attamey-George B. Oujevolk [5 7]ABSTRACT This dosimeter comprises a vessel having an inlet slit andoutlet slit for ultraviolet rays and a slit for releasing fluorescentlight beams which is opened in a direction almost perpendicularlyintersecting the direction in which the ultraviolet rays are introduced.In said vessel is housed a trapezoidal fluorescent glass element whoseoperating plane is exposed to radiation in advance and so positioned asto face the ultraviolet-ray inlet slit and fluorescent light beamrelease slit and also to be inclined at an angle allowing for the totalreflection of ultraviolet rays with respect to the direction in whichthey are brought in.

3 3 Drawing Figures Patented March 7, 1972 3,648,049

FIG. 1

\III H /L( hCL MI U INVENTORS DOSIMETER USING A FLUORESCENT GLASSELEMENT BACKGROUND OF THE INVENTION The present invention relates to adosimeter using a fluorescent glass element which is so improved as tobe adaptable for the quantitative determination of radioactive rays,particularly beta rays.

Glass prepared from silveractivated phosphate is generally known asfluorescent glass. Where this fluorescent glass is used in a dosimeterelement, there are raised the following problems. With the prior artdosimeter, the plane of a fluorescent glass element exposed to radiation(hereinafter referred to as the operating plane) is so positioned as tointersect at right angles the direction in which exciting ultravioletrays are brought in, and light beams from fluorescent nuclei are trappedby a detector disposed in a direction perpendicularly intersecting thatin which said fluorescent light beams travel. However, when thefluorescent glass element is exposed in advance to beta rays issued froma source of *TI having a low level energy, for example, a maximum energyof 0.764 Mev. and an average energy of 0.234 Mev., the aforementionedconventional dosimeter can only trap such amounts of fluorescent lightbeams as are equivalent to about one-thirtieth of those which arereleased when gamma rays from Co are irradiated on fluorescent glasselement under the same conditions. As generally understood, this is dueto the fact that said fluorescent glass originally has a nature ofcausing the amounts of fluorescent light beams generated by thefluorescent nuclei to sharply decrease from the level of around 3 to 5Mev.

On the other hand, exciting ultraviolet rays are stripped of raysbelonging to the visible region by means ofa filter before they areconducted to a fluorescent glass element. Depending on the compositionof such filter, however, there are still retained some amounts of raysbelonging to the red color region by the ultraviolet rays, insofar, asthe filter does not obstruct the transmission of said ultraviolet rays.

However, if red beam-bearing ultraviolet rays brought to the fluorescentglass element are reflected at random from the inner wall surface of thevessel, said red beams are also likely to be carried to a detector.While the ultraviolet rays can be removed by a shielding filterpositioned in front of the detector, the red beams contained in theultraviolet rays act on the detector as do the fluorescent light beamsto be determined, thus leading to erroneous issue of signals. This eventhas a serious effect on the determination of fluorescent light beamsassociated with beta rays having a low level energy, because the amountsof said fluorescent light beams are really small, and the quantitativedetermination thereof is sometimes made impossible.

Noticing the presence of a certain relationship between the energy levelof beta rays and the amount of fluorescent light beams issued from thefluorescent nuclei, the inventors have conducted a series of experimentsand as a result discovered that the fluorescent nuclei have such adistribution that with respect to the high energy level of beta rays,said nuclei extend from the exposed surface to the deeper part of thefluorescent glass element, whereas, in the case of the low energy levelof beta rays, the nuclei are concentrated in a shallow depth, forexample, about microns below the exposed surface.

SUMMARY OF THE INVENTION Based on the aforementioned fact, the presentinvention has been accomplished to improve a fluorescent glass elementand provide a dosimeter using such glass element wherein the position ofthe glass element in the vessel is so devised that even when the elementis exposed to beta rays of low energy level, sufficient amounts offluorescent light beams from the glass element can be effectivelytrapped by a detector and red beam-bearing ultraviolet rays can beprevented to the best possible extent from being conducted to thedetector.

Accordingly, the dosimeter of the present invention comprises a vesselhaving an inlet slit and outlet slit for ultraviolet rays and a slit forreleasing fluorescent light beams which is opened in a directionintersecting almost at right angles the direction in which ultravioletrays are introduced; means for supplying exciting ultraviolet rays tothe inlet slit therefor; means for detecting fluorescent light beamscoming through the release slit; and a fluorescent glass element whoseoperating plane is exposed to radiation in advance and so positioned asto face the ultraviolet-ray inlet slit and fluorescent light beamrelease slit and also to be inclined at an angle allowing for the totalreflection of ultraviolet rays with respect to the direction in whichthey are brought in, said fluorescent glass element having such anoptical plane as allows the ultraviolet rays to be totally reflectedthrough the outlet slit so as to prevent them from being again carriedthrough the operating plane of the glass element.

BRIEF EXPLANATION OF THE DRAWING FIG. 1 is a fragmental side section ofa dosimeter using a fluorescent glass device according to anembodimentof the present invention;

FIG. 2 is a fragmental side section of a dosimeter using a fluorescentglass device according to another embodiment of the invention; and

FIG. 3 is a perspective view illustrating the shape of a fluorescentglass element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, numeral 1represents a vessel for housing a fluorescent glass element 2 preparedfrom silver-activated phosphate glass. The vessel 1 as a whole assumes acylindrical form and has an inclined support plane 3 formed at thebottom. The opposing walls of the cylindrical vessel 1 are bored with aninlet slit 4 and outlet slit 5 for ultraviolet rays respectively, bothbeing positioned above the inclined support plane 3. The upper openingof the vessel 1 is used as a slit 6 for releasing fluorescent lightbeams. Above the vessel 1 are serially arranged an ultraviolet-rayshielding filter 7 and photon amplifier 8 in a manner to face thefluorescent light beam release slit 6. By the side of the vessel 1 isdisposed a super pressure mercury lamp (not shown), for example, a typedisplaying a continuous spectrum in which there appears the peak ofspectral energy at a wavelength of 365 millimicrons. Between the mercurylamp and vessel 1 is interposed a prescribed filter (not shown) sodesigned as the draw out ultraviolet rays whose wavelength ranges from345 to 380 millimicrons.

The fluorescent glass element 2 has a broader base plane or an operatingplane 2a exposed to beta rays and a side plane or an ultraviolet-rayinlet plane 2b which is made to face the ultraviolet-ray inlet slit 4when the glass element is placed in the vessel and intersect at rightangles the direction in which ultraviolet rays are brought in. On theopposite side of the glass element 2 to the ultraviolet-ray inlet plane2b is positioned another side plane or an ultraviolet-ray outlet plane2c for releasing ultraviolet rays in a manner to face the ultravioletrayoutlet slit 5.

The angle defined by the operating plane 20 with the ultraviolet-rayinlet plane 21; is set at a value allowing for the total reflection ofultraviolet rays, for example, at 70. It is advisable to dispose theoptical release plane 2c so as to perpendicularly intersect thedirection in which the ultraviolet rays reflected by the operating plane2a are allowed to proceed. A fluorescent glass element arranged asdescribed above assumes a trapezoidal form as illustrated. With respectto the shape of the optical release plane, there will be noinconvenience if said shape is so designed as to prevent reflectedultraviolet rays from being transmitted through the operating plane 2atoward the photon amplifier, even when they are optically brought backto said operating plane 2a.

Further, it is indispensable for the total reflection of exciting inletslit 4 that they be aligned into parallel beams by being allowed to passthrough a suitable relay lens and condenser lens.

Generally, radioactive rays include not only beta rays but also Xoraysand gamma rays. Accordingly, where beta rays are to be determined, thereare provided an aluminum filter 1.0 mrnv thick and plastics filterhaving a density of 7 mg./cm. respectively fitted to the operatingplanes of two fluorescent glass elements or the two divided regions ofthe operating plane of a simple fluorescent glass elementv Fluorescentlight beams released from the operating planes of the two fluorescentglass elements or the two divided regions of the operating plane ofasingle fluorescent glass element using the aforementioned two filtersrespectively are determined through the vessel using the photonamplifier 8, and the value of the d sage of beta computed from thedifference between the two determinations thus obtained is furtherconverted to a proper value on the basis ofthe previously defined valueof the amounts of beta rays emitted from natural uranium (U when used asa source of beta rays.

Parallel ultraviolet rays are conducted to the fluorescent glass elementthrough the aforesaid inlet plane 2b to be totally reflected from theoperating plane of said glass element with the resultant substantiallycomplete withdrawal of the ultraviolet rays from the outlet plane 20.The released ultraviolet rays cause fluorescent light beams to beprojected by the fluorescent nuclei concentrately distributed in theshallow region below the operating plane 2a. These fluorescent lightbeams are allowed to pass through the release slit 6 to be trapped bythe photon amplifier 8. In this case, not only fluorescent nuclei can beefficiently excited by the flux of fully released ultraviolet rays dueto the inclined position of the operating plane 2a, but also fluorescentlight beams projected by the fluorescent nuclei distributed right belowthe operating plane 2a can be effectively trapped by the photonamplifier, because the operating plane also faces said amplifier 8.Further the present invention permits the total reflection ofultraviolet rays and almost prevents red beams from being conducted tothe photon amplifier 8 through the operating plane 2a so that theinvention has an effect of substantially eliminating the occurrence oferrors in determining the amounts offluorescent light beams.

To describe the feature of the dosimeter of the present invention havingthe aforementioned arrangement, let us take the example of determiningbeta rays from T1 by irradiating them on a fluorescent glass elementthrough a material corresponding to an epidermis having a density of 7mg./crn. in this determination the amount of fluorescent light beamsresulting from said beta rays prominently increased per rad of softhuman tissue to 49 times the per rad amount of fluorescent light beamsgenerated by gamma rays from Co when they were irradiated on afluorescent glass element 8 8 .7 mm.

FIG. 2 illustrating another embodiment presents the condition ofdetermination where the operating plane 20 is positioned on the oppositeside of the fluorescent glass element 2 to the fluorescent light beamamplifier 8. The essential function of this embodiment does not vary atall from that of the aforementioned embodiment. it will be noted,however, that for the determination according to the embodiment of FIG.2, the inlet slit 4 and outlet slit 5 for ultraviolet rays arepositioned with respect to the level in the opposite relationship towhat is observed in FIG. 1 and fluorescent light beams are conducted tothe photon amplifier 8 through the opposite plane of the fluorescentglass element to the operating plane 2a thereof and released ultravioletrays are prevented from being reflected back to that opposite plane.

What is claimed is:

l. A dosimeter using a fluorescent glass element which comprises anelongated longitudinal vessel having an inlet slit (4) on one side ofthe vessel and outlet slit (5) on the other side of the vessel butoffset from said inlet slit for ultraviolet rays and a release slit (6)for releasing fluorescent light beams opening in a directionintersecting substantially at right angles the direction in which theultraviolet rays are brought in; excitation means for suppllyingexciting ultraviolet ra s to said inlet slit; an ultraviolet iter (7)and photon ampli ier means (8) for detecting fluorescent light beamscarried through said release slit; and a fluorescent glass element (2)having a trapezoidal cross section whose operating plane is so disposedin the vessel as to face the ultraviolet-ray inlet slit and fluorescentlight beam release slit and also to be inclined at an angle towards theoutlet slit allowing for the total reflection of ultraviolet rays withrespect to the direction in which they are introduced, said fluorescentglass element having such an ultraviolet outlet plane as releases thetotally reflected ultraviolet rays from the outlet slit in a manner toprevent them from being carried again through the operating plane oropposite plane thereto of said glass element.

2. The dosimeter according to claim 1 wherein the ultraviolet outletplane is formed perpendicular to the direction in which the reflectedultraviolet rays are released.

3. in a dosimeter using a fluorescent glass element, in combination: anelongated longitudinal vessel having an inlet slit (4) on one side ofthe vessel and outlet slit (5) on the other side of the vessel butoffset from said inlet slit for ultraviolet rays and a release slit forreleasing fluorescent light beams opening in a direction intersectingsubstantially at right angles the direction in which the ultravioletrays area brought in; excitation means for supplying excitingultraviolet rays to said inlet slit; and a fluorescent glass element (2)having a trapezoidal cross section whose operating plane is so disposedin the vessel as to face the ultraviolet-ray inlet slit and fluorescentlight beam release slit and also to be inclined at an angle towards theoutlet slit allowing for the total reflection of ultraviolet rays withrespect to the direction in which they are introduced, said fluorescentglass element having such an ultraviolet outlet plane as releases thetotally reflected ultraviolet rays from the outlet slit in a manner toprevent them from being carried again through the operating plane oropposite plane thereto ofsaid glass element.

1. A dosimeter using a fluorescent glass element which comprises anelongated longitudinal vessel having an inlet slit (4) on one side ofthe vessel and outlet slit (5) on the other side of the vessel butoffset from said inlet slit for ultraviolet rays and a release slit (6)for releasing fluorescent light beams opening in a directionintersecting substantially at right angles the direction in which theultraviolet rays are brought in; excitation means for supplying excitingultraviolet rays to said inlet slit; an ultraviolet filter (7) andphoton amplifier means (8) for detecting fluorescent light beams carriedthrough said release slit; and a fluorescent glass element (2) having atrapezoidal cross section whose operating plane is so disposed in thevessel as to face the ultraviolet-ray inlet slit and fluorescent lightbeam release slit and also to be inclined at an angle towards the outletslit allowing for the total reflection of ultraviolet rays with respectto the direction in which they are introduced, said fluorescent glasselement having such an ultraviolet outlet plane as releases the totallyreflected ultraviolet rays from the outlet slit in a manner to preventthem from being carried again through the operating plane or oppositeplane thereto of said glass element.
 2. The dosimeter according to claim1 wherein the ultraviolet outlet plane is formed perpendicular to thedirection in which the reflected ultraviolet rays are released.
 3. In adosimeter using a fluorescent glass element, in combination: anelongated longitudinal vessel having an inlet slit (4) on one side ofthe vessel and outlet slit (5) on the other side of the vessel butoffset from said inlet slit for ultraviolet rays and a release slit forreleasing fluorescent light beams opening in a direction intersectingsubstantially at right angles the direction in which the ultravioletrays area brought in; excitation means for supplying excitingultraviolet rays to said inlet slit; and a fluorescent glass element (2)having a trapezoidal cross section whose operating plane is so disposedin the vessel as to face the ultraviolet-ray inlet slit and fluorescentlight beam release slit and also to be inclined at an angle towards theoutlet slit allowing for the total reflection of ultraviolet rays withrespect to the direction in which they are introduced, said fluorescentglass element having such an ultraviolet outlet plane as releases thetotally reflected ultraviolet rays from the outlet slit in a manner toprevent them from being carried again through the operating plane oropposite plane thereto of said glass eLement.